The company also said the drug candidate prompted a response in a key protein for patients in the study, though that was not the study’s main goal. The results are only preliminary, Vertex said.

The study involves 89 patients receiving one of four doses of VX-809, or placebo, in addition to standard therapies, for 28 days.

The company plans on moving forward with combining VX-809 with its other experimental cystic fibrosis drug, VX-770, for additional studies in the second half of 2010.

Cystic fibrosis causes a fluid imbalance in the lungs, resulting in mucus plugging, infection and inflammation. It affects about 30,000 people in the U.S. and around 70,000 people worldwide, the company has said.